The present invention relates to a light amount-adjusting device for use in an imaging device such as a camera or in a projecting device such as a projector. More particularly, the invention relates to a light amount-adjusting device such as an aperture device for adjusting the light amount in an optical path or a shutter device for blocking the light amount. The invention also relates to a light amount-adjusting device for use in a projector unit using such a device.
Generally, a light amount-adjusting device of this kind is widely known as a device which is incorporated in a lens barrel such as an imaging lens or projector lens and which is used to adjust the amount of light according to the circumstances of use. A related art device of this kind has been so configured that one or more blades are mounted in a base plate provided with an aperture formed in an optical path. The blades are swung open and closed by a driving motor, thus performing a shutter operation or an operation,for restricting the amount of light.
Such a light amount-adjusting device has a base plate molded from a synthetic resin, as disclosed, for example, in a patent reference JP-A-2003-57715. Shaft pins are mounted on the base plate. Base-end portions of plural blade members are securely supported to the shaft pins. The blade members are arranged at a given interval around the aperture. Front-end portions of the blade members stop down the aperture to a variable extent or shut off the aperture by rotating the blade members by the same amount. A holding plate is mounted like a cover over the base plate. The blade members are positioned between the base plate and the holding plate so as to be capable of being swung open and closed.
Where the plural blade members are superimposed like fish scales over the base plate forming the aperture in the optical path as described above and are swung open and closed, the following structure has been heretofore adopted. A second blade is stacked on a first blade, and then the holding plate is placed on the topmost blade. Therefore, the blades superimposed vertically frequently interfere with each other, resulting in malfunction. Especially, if the blades are distorted by temperature or external shock, the blades mesh with each other, making the device inoperative. Another problem is that friction between the blades hinders them from being smoothly swung open and closed.
Accordingly, a structure having a base plate with rib-like protrusions which support the first and second blades, respectively, is known as disclosed in the above-cited patent reference. A difference in heightwise position corresponding to the thickness of each blade is created between the two protrusions. However, if the protrusions that alleviate the interference (friction) between the blades are formed on the base plate supporting the blades in this way, the following problem arises. Where the blades are made of metal sheet less affected by temperature variations and undergoing less aging variations, for example, the blades themselves are large in mass. If an attempt is made to swing open and closed the blades at high speed, the blades are swung up and down perpendicularly to the longitudinal direction of the blades by vibrations. Consequently, the operation is unstable and generates noise. Also, malfunction may occur.
In view of the foregoing mutual motion between the blades, it is a main object of the invention to provide a light amount-adjusting device which prevents plural blades superimposed vertically from interfering with each other to thereby prevent failure of operation. The light amount-adjusting device also prevents the blades from producing noise when swung open and closed. In the light amount-adjusting device, low frictional load occurs when the blades are swung open and closed.
Further objects and advantages of the invention will be apparent from the following description of the invention and the associated drawings.